A sour hydrocarbon gas extracted from a gas field has to undergo several treatments to meet specific constraints dictated by commercial or security specifications. These treatments include for instance deacidification, dehydration, and liquefaction. Concerning H2S and other sulphur compounds, such as mercaptans, levels of few ppm are imposed for the treated gas.
Therefore, when a sour gas has a high content in mercaptans, it may requires further treatment of some gas or liquid cuts such as liquefied petroleum gas (LPG) in order to meet the commercial or security specifications. In that case, mercaptans may be removed by using a caustic solution which however produces an unwanted by-product named disulfide oil (DSO) which is composed of a mixture of dialkyldisulfides. To solve this problem, the most common practice is to mix DSO with large amount of condensate or oil if compatible with their specification. However, liquid production of gas is not always available onsite or there may be not enough liquid to mix with DSO. Therefore, DSO disposal is a very crucial issue in such fields.
FR 2875236 discloses a method for removing DSO comprising the hydrogenation of DSO wherein DSO is converted into H2S and hydrocarbons. This method uses pure hydrogen in order to perform hydrogenation of vaporized DSO. It also requires a specific plant dedicated to DSO wherein DSO is vaporized, hydrogen is produced or imported, and hydrogenation of DSO into H2S is performed. However, this process incurs a lot of capital expenditure (CAPEX). Furthermore, pure hydrogen is not always available at the site and needs to be imported or requires a hydrogen plant.
Therefore, there is need for a method for removing DSO within a process for treating a sour gas that is simpler and has a lower CAPEX.